A bungee-jumper of mass m is attached by means of a light rope of natural length l and modulus of elasticity (mg)/k, where k is a constant, to a bridge over a ravine. She jumps from the bridge and falls vertically towards the ground. Ignoring air resistance, find her speed when the rope becomes taut. If she only just avoids hitting the ground, show that the height h of the bridge above the floor of the ravine satisfies:

(h^2)-2hl(k+1)+(l^2)=0.

No idea where to start, please help. Please also explain what the modulus of elasticity is. Thanks.